A reclassification of Northwest Africa 2900 from CV3 to CK3 chondrite

• Published in: Meteoritics & planetary science 2020-11, Vol.55 (11), p.2539-2550
• Main Authors: Torrano, Zachary A., Davidson, Jemma, Wadhwa, Meenakshi
• Format: Article
• Language: English
• Subjects: Abundance; Aluminum oxide; Chondrites; Chondrule; Chromium oxides; Classification; Evaluation; Iron content; Isotope composition; Isotopes; Magnetite; Nickel oxides; Olivine; Oxygen; Oxygen isotopes; Similarity; Titanium dioxide
• ISSN: 1086-9379; 1945-5100
• DOI: 10.1111/maps.13587

The similarities between CV and CK chondrites are so substantial that some studies have argued for a common parent body origin. These similarities also mean that they are susceptible to misclassification as one another. It is, therefore, important to accurately classify CV and CK chondrites to properly compare the properties of the two groups and evaluate the single parent body hypothesis. In this study, we re‐evaluate the current classification of Northwest Africa (NWA) 2900 as a CV3 chondrite. Based on chondrule abundance (~13%), average chondrule diameter (1.11 ± 0.67 mm), iron content in chondrule olivine (Fa1 to Fa35 with a peak near ~Fa31) and matrix olivine (Fa33 to Fa36), magnetite abundance (~4 vol%), elemental abundances in olivine (Cr2O3, Al2O3, TiO2, MnO, NiO, and CaO) and magnetite (Cr2O3, Al2O3, TiO2, and NiO), and comparison with previously reported data for CV and CK chondrites, we propose that the classification of NWA 2900 be changed from CV3 chondrite to CK3 chondrite, with characteristics most similar to those of the CK3.8 subtype. We additionally suggest minor modifications to the compositional criteria used to distinguish between CV and CK chondrites and demonstrate that NWA 2900 extends the range of bulk oxygen isotope compositions of CK chondrites.